1. Field of the Invention
This invention relates to a system for measuring and displaying unbalance in a rotating body and more particularly to such a system which has the capability of measuring and providing correction quantities for system imposed unbalanced measurement errors.
2. Description of the Prior Art
U.S. Pat. No. 4,285,240, Gold, issued Aug. 25, 1981 discloses an off-the-car wheel unbalance measuring system having a rotationally driven wheel mounting shaft supported in a pedestal. A pair of force transducers are mounted in the pedestal adjacent to and spaced axially along the shaft. The force transducers are coupled mechanically to the shaft and provide periodic electrical output signals indicative of unbalance forces transmitted through the shaft when the shaft is driven rotationally. The angular position of the shaft is monitored with respect to an angular reference position at a predetermined number of angular increments during each full revolution of the shaft. The transducer output signals are converted to digital form in electrical circuitry within the system and calculations are performed on the digitized signals at each angular increment using sine and cosine representative factors corresponding to the particular angular increment. The sine and cosine factors are stored in memory and are called up from storage in accordance with the monitored angular position of the shaft. This system operates to provide operating data from which unbalance force magnitude and angular position may be calculated. Operation of the system while a known unbalance is mounted on the shaft provides data from which calibration constants for the system may be calculated. The system may also be operated while the shaft is running free and data collected which is indicative of the unbalance in the shaft itself. These data may thereafter be used to provide error correction for operating data wherein the errors accrue from transducer idiosyncrasies and/or inherent shaft unbalance.